I am sure it is related to graphics in some way. 320 and 240, my mind always links those numbers to graphics although they could be anything but other variables that have already been identified as graphics related pop up in routines it calls, so it must be graphics related.

Down into the "some_bookkeeping_A" there is stuff that looks like a heap or like a data structure where individual fields of the structure are stored in separate arrays of 460 words each. One of the arrays ([bx-71BAh]) appears to contain bitflags of which the highest bit seems to mark an item as "occupied" or "in use".

The other flags in there perhaps mark the resource type of the graphic item or the resource type in general or maybe even tell how it is supposed to be decoded, because the bits are used to branch into different subroutines.

Current notes that I keep open on the side. Unfortunately, IDA does not allow to assign names to computed addresses, so I have to rely on my eyes' pattern matching abilities on these to not miss anything. Having all the numbers opened on the side helps with that.